Extreme Ultraviolet Photoresist With High-Efficiency Electron Transfer

ABSTRACT

A method includes forming a photoresist layer over a substrate, wherein the photoresist layer includes a polymer, a sensitizer, and a photo-acid generator (PAG), wherein the sensitizer includes a resonance ring that includes nitrogen and at least one double bond. The method further includes performing an exposing process to the photoresist layer. The method further includes developing the photoresist layer, thereby forming a patterned photoresist layer.

PRIORITY INFORMATION

This application claims the benefit of U.S. Provisional PatentApplication No. 62/434,961 filed Dec. 15, 2016, and entitled “ExtremeUltraviolet Photoresist with High-Efficiency Electron Transfer,” thedisclosure of which is hereby incorporated by reference in its entirety.

BACKGROUND

The semiconductor integrated circuit (IC) industry has experiencedexponential growth. Technological advances in IC materials and designhave produced generations of ICs where each generation has smaller andmore complex circuits than the previous generation. In the course of ICevolution, functional density (i.e., the number of interconnecteddevices per chip area) has generally increased while geometry size(i.e., the smallest component (or line) that can be created using afabrication process) has decreased. This scaling down process generallyprovides benefits by increasing production efficiency and loweringassociated costs. Such scaling down has also increased the complexity ofprocessing and manufacturing ICs.

For example, as the semiconductor fabrication continues to shrinkpitches below 20 nm nodes, traditional i-ArF photoresists confronted ahuge challenge. The optical restriction leads to resolution andlithography performance that cannot meet targets. Extreme ultraviolet(EUV) lithography has been utilized to support critical dimension (CD)requirements of smaller devices. EUV lithography employs scanners usingradiation in the EUV region, having a wavelength of about 1 nm to about100 nm. Some EUV scanners provide 4× reduction projection printing ontoa resist film coated on a substrate, similar to some optical scanners,except that the EUV scanners use reflective rather than refractiveoptics. EUV lithography has imposed a complex set of requirements uponthe resist film.

The photo acid generator (PAG) in ArF resist absorbs 193 nm wave andgenerates photoacid, and the acid will proceed 1000 times chemicalamplifier reaction (CAR) and deprotect acid labile group (ALG).Different with 193 nm ArF resist, EUV will let sensitizer generatesecondary electron. The secondary electron's energy is similar with 193nm energy and is absorbed by PAG, which further generates photoacid andproceeds to CAR reaction after absorbing secondary electron, like 193 nmArF resist. However, the EUV resist still suffers energy efficiency andother related issues due to chemical structure of known sensitizers, lowsource power for EUV tool, and factors. What are needed are aphotoresist and a method using the photoresist to have improvements inthis area.

BRIEF DESCRIPTION OF THE DRAWINGS

The present disclosure is best understood from the following detaileddescription when read with the accompanying figures. It is emphasizedthat, in accordance with the standard practice in the industry, variousfeatures are not drawn to scale and are used for illustration purposesonly. In fact, the dimensions of the various features may be arbitrarilyincreased or reduced for clarity of discussion.

FIGS. 1A-1C illustrate a process for lithography patterning withphotoresist having increased sensitivity to EUV light, according to oneexample of principles described herein.

FIG. 2 is a diagram showing illustrative components of a photoresistthat has increased sensitivity to EUV light, according to one example ofprinciples described herein.

FIGS. 3A and 3B illustrate various characteristics of a sensitizer for aphotoresist with increased sensitivity to EUV light, according to oneexample of principles described herein.

FIG. 4 is a diagram showing an illustrative polymer structure that maybe used in a photoresist with increased sensitivity to EUV light,according to one example of principles described herein.

FIG. 5 is a diagram showing an illustrative blocking structure that maybe used in a photoresist with increased sensitivity to EUV light,according to one example of principles described herein.

FIGS. 6A and 6B show illustrative chemical structures of a sensitizerfor a photoresist with increased sensitivity to EUV light, according toone example of principles described herein.

FIGS. 7A, 7B, 7C, and 7D show illustrative chemical structures of a PAGfor a photoresist with increases sensitivity to EUV light, according toone example of principles described herein.

FIGS. 8A, 8B, 8C, 8D, 8E, 8F, 8G, and 8H show additional illustrativechemical structures of a PAG for a photoresist with increasessensitivity to EUV light, according to one example of principlesdescribed herein.

FIG. 9 is a flowchart showing an illustrative method of using aphotoresist having a sensitizer that improves the photoresist'ssensitivity to EUV light, according to one example of principlesdescribed herein.

FIG. 10 is a flowchart showing an illustrative method of using aphotoresist having a PAG that improves the photoresist's sensitivity toEUV light, according to one example of principles described herein.

DETAILED DESCRIPTION

The following disclosure provides many different embodiments, orexamples, for implementing different features of the provided subjectmatter. Specific examples of components and arrangements are describedbelow to simplify the present disclosure. These are, of course, merelyexamples and are not intended to be limiting. For example, the formationof a first feature over or on a second feature in the description thatfollows may include embodiments in which the first and second featuresare formed in direct contact, and may also include embodiments in whichadditional features may be formed between the first and second features,such that the first and second features may not be in direct contact. Inaddition, the present disclosure may repeat reference numerals and/orletters in the various examples. This repetition is for the purpose ofsimplicity and clarity and does not in itself dictate a relationshipbetween the various embodiments and/or configurations discussed.

Further, spatially relative terms, such as “beneath,” “below,” “lower,”“above,” “upper” and the like, may be used herein for ease ofdescription to describe one element or feature's relationship to anotherelement(s) or feature(s) as illustrated in the figures. The spatiallyrelative terms are intended to encompass different orientations of thedevice in use or operation in addition to the orientation depicted inthe figures. The apparatus may be otherwise oriented (rotated 90 degreesor at other orientations) and the spatially relative descriptors usedherein may likewise be interpreted accordingly.

The present disclosure is generally related to methods for semiconductordevice fabrication, and more particularly to compositions ofphotosensitive films in extreme ultraviolet (EUV) lithography andmethods of using the same. In lithography patterning, after a resistfilm is exposed to a radiation, such as a EUV radiation (oralternatively other radiation, such as an electron beam), it isdeveloped in a developer (a chemical solution). The developer removesportions (such as exposed portions as in a positive-tone photoresist orunexposed portions as in a negative-tone photoresist) of the resistfilm, thereby forming a resist pattern which may include line patternsand/or trench patterns. The resist pattern is then used as an etch maskin subsequent etching processes, transferring the pattern to anunderlying material layer. Alternatively, the resist pattern is thenused as an ion implantation mask in subsequent ion implantationprocesses applied to the underlying material layer, such as an epitaxialsemiconductor layer.

Generally, to produce the smallest possible circuitry, most advancedlithography systems are designed to use light of very short wavelengthsuch as for example, deep-ultraviolet light at a wavelength at or below200 nm, or extreme ultraviolet (EUV) with a wavelength of about 13.5 nm.Such light sources are relatively weak, so the photosensitive films(e.g., a photoresist) need to be designed to utilize this light asefficiently as possible.

A photoresist that employs the chemical amplification is generallyreferred to as a “chemically amplified resist (CAR)”. A photoresistincludes a polymer that resists etching or ion implantation duringsemiconductor fabrication. The photoresist also includes an acidgenerating compound (e.g., photo acid generator (PAG)), and a solvent.In some examples, the polymer also includes at least one acid labilegroup (ALG) that responds to acid. PAG absorbs radiation energy andgenerates acid. The polymer and the PAG are mixed in the solvent beforethe photoresist is applied to a workpiece, such as a semiconductorwafer, during a lithography process. The PAG is not sensitive to the EUVradiation. That is, advances to improve lithography efficiency (e.g.,resolution/contrast, line-width-roughness, and sensitivity) encounterissues.

According to the present disclosure, the photoresist includes asensitizer with a relatively high recombination energy and a lowionization energy. The sensitizer, when exposed to EUV light emitselectrons. More specifically, the sensitizer absorbs EUV radiation andgenerates electrons. These electrons may then trigger the acidgeneration from the PAG. According to one example of principlesdescribed herein, the sensitizer has a chemical structure that hasspecific properties that increase the efficiency of the sensitizer.First, the sensitizer includes a low electron ionization energy. Thismeans that it takes less energy absorbed from the EUV to generate anelectron. Second, the sensitizer has a relatively high recombinationenergy level. This means that it is more difficult for the electron torecombine with the sensitizer. This is desirable because it is betterthat the electron not be recombined but instead travel to a PAGstructure to trigger acid generation. Additionally, the PAG may includea structure that it makes it more efficient at absorbing the electron totrigger acid generation.

In one example, the desirable characteristics of the sensitizer areachieved by having a chemical structure with a heterocyclic ring thatincludes at least one nitrogen atom and at least one double bond.Additionally, the desirable characteristics of the PAG may be achievedby having an absorb group with at least one ring that is heterocyclicwith a carbon atom and at least one nitrogen or oxygen atom Suchstructures, as described in more detail below, allow for more efficientelectron transfer and more efficient acid generation under EUVradiation. The photoresist and the lithography methods are furtherdescribed below.

FIGS. 1A-1C illustrate a process for lithography patterning withphotoresist having increased sensitivity to EUV light. As describedabove, the photoresist has increased sensitivity to EUV light due to thesensitizer having a higher recombination energy level and a lowerionization energy and the PAG having better absorption of electrons.FIG. 1A illustrates a photoresist layer 104 deposited onto asemiconductor structure 100. The semiconductor structure 100 may be anintermediate workpiece fabricated during processing of an IC, or aportion thereof, that may include logic circuits, memory structures,passive components (such as resistors, capacitors, and inductors), andactive components such diodes, field-effect transistors (FETs),metal-oxide semiconductor field effect transistors (MOSFET),complementary metal-oxide semiconductor (CMOS) transistors, bipolartransistors, high voltage transistors, high frequency transistors,fin-like FETs (FinFETs), other three-dimensional (3D) FETs, metal-oxidesemiconductor field effect transistors (MOSFET), complementarymetal-oxide semiconductor (CMOS) transistors, bipolar transistors, highvoltage transistors, high frequency transistors, other memory cells, andcombinations thereof.

According to the present example, the semiconductor structure 100includes a substrate 102. In one example, the substrate 102 is asemiconductor substrate (e.g., wafer). In another example, the substrate102 includes silicon in a crystalline structure. In alternativeembodiments, the substrate 102 includes other elementary semiconductorssuch as germanium, or a compound semiconductor such as silicon carbide,gallium arsenide, indium arsenide, and indium phosphide. The substrate102 may include one or more layers of material or composition. Thesubstrate 102 may include a silicon on insulator (SOI) substrate, bestrained/stressed for performance enhancement, include epitaxialregions, include isolation regions, include doped regions, include oneor more semiconductor devices or portions thereof, include conductiveand/or non-conductive layers, and/or include other suitable features andlayers.

In the present example, the substrate 102 is to be processed so as to bepatterned or to be implanted. In some examples, an underlayer (notshown), such as a hard mask, may be deposited onto the substrate 102before the resist layer 104 is deposited. In one example, the underlayermay include material(s) such as silicon oxide, silicon nitride (SiN),silicon oxynitride, or other suitable material or composition. In someexamples the underlayer is an anti-reflection coating (ARC) layer suchas a nitrogen-free anti-reflection coating (NFARC) layer includingmaterial(s) such as silicon oxide, silicon oxygen carbide, or plasmaenhanced chemical vapor deposited silicon oxide. In some examples, theunderlayer may include a high-k dielectric layer, a gate layer, a hardmask layer, an interfacial layer, a capping layer, a diffusion/barrierlayer, a dielectric layer, a conductive layer, other suitable layers,and/or combinations thereof.

In some examples, the semiconductor structure 100 may be alternatively aphotomask used to pattern a semiconductor wafer. In furtherance of suchexamples, the substrate 102 is a photomask substrate that may include atransparent material (such as quartz), or a low thermal expansionmaterial such as silicon oxide-titanium oxide compound. The photomasksubstrate may further include a material layer to be patterned. Tofurther this example, the substrate may be a photomask substrate formaking a deep ultraviolet (DUV) mask, an extreme ultraviolet (EUV) mask,or other types of masks. Accordingly, the underlayer may be a materiallayer to be patterned to define a circuit pattern. For example, theunderlayer may be an absorber layer, such as chromium layer.

The resist layer 104 is sensitive to radiation used in a lithographyexposure process and has a resistance to etch (or implantation). Theresist layer 104 may be formed by a spin-on coating process. In someexamples, the photoresist is further treated with a soft baking process.In some examples, the resist layer 104 is sensitive to a radiation, suchas I-line light, a DUV light (e.g., 248 nm radiation by krypton fluoride(KrF) excimer laser or 193 nm radiation by argon fluoride (ArF) excimerlaser), a EUV light (e.g., 135 nm light), an electron beam (e-beam), andan ion beam. In the present example, the photoresist layer is sensitiveto EUV radiation.

FIG. 1B illustrates an exposing process 108 to expose the resist layer104 to a radiation beam in a lithography system. In some examples, theradiation is an EUV radiation (e.g., 13.5 nm). In some examples, theradiation may be an I-line (365 nm), a DUV radiation such as KrF excimerlaser (248 nm), ArF excimer laser (193 nm), a EUV radiation, an x-ray,an e-beam, an ion beam, and/or other suitable radiations. The exposingprocess 108 may be performed in air, in a liquid (immersionlithography), or in a vacuum (e.g., for EUV lithography and e-beamlithography). In some examples, the radiation beam is directed to theresist layer 104 to form an image of a circuit pattern defined on aphotomask, such as a transmissive mask or a reflective mask in a properexposing mode, such as step and scan. Various resolution enhancementtechniques, such as phase-shifting, off-axis illumination (OAI) and/oroptical proximity correction (OPC), may be used implemented through thephotomask or the exposing process. For examples, the OPC features may beincorporated into the circuit pattern. In another example, the photomaskis a phase-shift mask, such as an alternative phase-shift mask, anattenuated phase-shift mask, or a chromeless phase-shift mask. In yetanother example, the exposing process is implemented in an off-axisillumination mode. In some other embodiments, the radiation beam isdirectly modulated with a predefined pattern, such as an IC layout,without using a mask (such as using a digital pattern generator ordirect-write mode). In the present embodiment, the radiation beam is aEUV radiation and the exposing process 108 is performed in an EUVlithography system, such as the EUV lithography system. Since thesensitivity of the resist layer 104 is enhanced and the exposingthreshold of the resist layer may be lower than 20 mJ/cm². Accordingly,the exposing process is implemented with the dose less than 20 mJ/cm².

Due to the particular properties of the resist layer 104, the resistlayer 104 more efficiently absorbs EUV light. More specifically, moreelectrons are generated by the sensitizer. These electrons are then moreefficiently absorbed by the PAG.

After the exposing process, there may be thermal treatments in somecases. For example, a post-exposure baking (PEB) process may be appliedto the semiconductor structure 100, especially to the resist layer 104coated on the substrate 102. During the PEB process, the ALG in theexposed resist material is cleaved, the exposed portions of the resistmaterial are changed chemically (such as more hydrophilic or morehydrophobic). In a specific embodiment, the PEB process may be performedin a thermal chamber at temperature ranging between about 120° C. toabout 160° C.

After the exposing process 108, the exposed portions 110 are chemicallyaltered such that they will either be resistant to a developer orremovable by a developer. In some examples, the exposed portions 110 arede-protected, inducing polarity change for dual-tone imaging(developing). In other examples, the exposed portions 110 are changed inpolymerization, such as depolymerized as in positive resist orcross-linked as in negative resist.

FIG. 1C illustrates a development process applied to the resist layer104. By the developing process, a patterned resist layer 112 is formed.In some examples, the resist layer 104 experiences a polarity changeafter the exposing process 108, and a dual-tone developing process maybe implemented. In some examples, if the resist layer 104 is changedfrom a nonpolar state (hydrophobic state) to a polar state (hydrophilicstate), then the exposed portions 110 will be removed by an aqueoussolvent (positive tone imaging), such as tetramethyl ammonium hydroxide(TMAH), or alternatively the unexposed portions will be removed by anorganic solvent (negative tone imaging), such as butyl acetate. In someother examples, the resist layer 104 is changed from a polar state to anonpolar state, then the exposed portions 110 will be removed by anorganic solvent (positive tone imaging) or the unexposed portions willbe removed by an aqueous solvent (negative tone imaging).

In the present example illustrated in FIG. 1C, the exposed portions 110are removed in the developing process 114. In this example shown in FIG.1C, the patterned resist layer 112 is represented by two line patterns.However, the following discussion is equally applicable to resistpatterns represented by trenches.

In some examples, a fabrication process, such as an etch or implantationprocess, may be applied to the semiconductor structure 100 using thepatterned resist layer 112 as a mask such that the fabrication processis only applied to the portions of the semiconductor structure 100within the openings of the patterned resist layer 112 while otherportions covered by the patterned resist layer 112 are protected frombeing impacted by the fabrication process. In some examples, thefabrication process includes an etching process applied to the materiallayer 102 using the patterned resist layer 112 as an etch mask, therebytransferring the pattern from the patterned resist layer 112 to thematerial layer 102. In some examples, the fabrication process includesan ion implantation process applied to the semiconductor structure 100using the patterned resist layer as an implantation mask, therebyforming various doped features in the semiconductor structure 100.

In the case where a hard mask layer is positioned above the materiallayer 102, the pattern is first transferred from the patterned resistlayer 112 to the hard mask layer, and then to the material layer 102.For example, the hard mask layer may be etched through openings of thepatterned resist layer 112 using a dry (plasma) etching, a wet etching,and/or other etching methods. For example, a dry etching process mayimplement an oxygen-containing gas, a fluorine-containing gas, achlorine-containing gas, a bromine-containing gas, an iodine-containinggas, other suitable gases and/or plasmas, and/or combinations thereof.The patterned resist layer 112 may be partially or completely consumedduring the etching of the hard mask layer. In one example, any remainingportion of the patterned resist layer 112 may be stripped off, leaving apatterned hard mask layer over the substrate 102.

Although not shown in FIGS. 1A to 1C, the fabrication process mayinclude other operations before, during or after the operationsdescribed above. In one example, the other operations may includeforming field effect transistor (FinFET) structures. In such an example,the fabrication process may include forming a plurality of active finsin the semiconductor substrate 102. In furtherance of this example,substrate 102 may be etched through the openings of the patterned hardmask to form trenches in the substrate 102; filling the trenches with adielectric material; performing a chemical mechanical polishing (CMP)process to form shallow trench isolation (STI) features; and epitaxygrowing or recessing the STI features to form fin-like active regions.In some examples, the other operations may include forming a pluralityof gate electrodes in the semiconductor substrate 102. Other operationsmay further include forming gate spacers, doped source/drain regions,contacts for gate/source/drain features, etc. In some examples, a targetpattern is to be formed as metal lines in a multilayer interconnectionstructure. For example, the metal lines may be formed in an inter-layerdielectric (ILD) layer of the substrate 102, which has been etched by toform a plurality of trenches. Other operations may include filling thetrenches with a conductive material, such as a metal; and furtherpolishing the conductive material using a process such as chemicalmechanical planarization (CMP) to expose the patterned ILD layer,thereby forming the metal lines in the ILD layer. The above arenon-limiting examples of devices/structures that can be made and/orimproved using the resist layer 104 according to various aspects of thepresent disclosure.

FIG. 2 is a diagram showing illustrative components of a photoresistthat has increased sensitivity to EUV light. In the present example, thephotoresist 300 utilizes a chemical amplification (CA) photoresistmaterial. In one example, the CA resist material is positive tone andincludes a polymer material that turns soluble to a developer after thepolymeric material is reacted with acid. In another example, the CAresist material is negative tone and includes a polymer material thatturns insoluble to a developer such as a base solution after the polymeris reacted with acid. In yet another example, the CA resist materialincludes a polymer material that changes its polarity after the polymeris reacted with acid.

The resist material 200 is sensitive extreme ultraviolet (EUV) light.The resist material 200 includes a polymer 202, a blocking group 204chemically bonded to the polymer 202, a sensitizer 206, and an AcidGenerating Compound (AGC) such as a Photo-Acid Generator (PAG) 208. Theresist material 200 further includes solvent 210 with the abovechemicals mixed therein. The sensitizer 206 may be blended with orbonded to the polymer 202, or bonded to the AGC 208. In someembodiments, the resist material 200 may include other additives, suchas quencher.

The polymer 202 provides resistance to etch (or implantation). Invarious examples, the polymer 202 includes a poly(norbornene)-co-malaicanhydride (COMA) polymer, a polyhydroxystyrene (PHS) polymer, or anacrylate-based polymer. For example, the acrylate-based polymer includesa poly (methyl methacrylate) (PMMA) polymer. The PHS polymer includes aplurality of PHS chemical structure 400 shown in FIG. 4, in which n isan integer greater than 2. The PHS chemical structure 400 includes twoends 402 and 404 that are chemically linkable ends of other PHS chemicalstructures. Furthermore, PHS is also sensitive to EUV and is able tofunction as sensitizer for EUV resist. Accordingly, a plurality of thechemical structures 400 are chemically bonded together (through the twoends 402 and 404), thereby forming a PHS polymeric backbone. The polymer202 also includes multiple side locations that may chemically bond withother chemical groups. For example, the PHS polymer includes a pluralityof hydroxyl (OH) groups 406 chemically bonded to side locations.

In some examples, the resist material 200 further includes a blockinggroup 204, such as acid labile group (ALG) or dissolution inhibitor thatresponds to acid. The blocking group 204 is a chemical group that isdeprotected by PAG in exposed areas of the resist layer. Thus, theexposed resist material 200 will change the polarity and dissolubility.For example, the exposed resist material has an increased dissolubilityin a developer (for a positive-tone resist) or decreased dissolubilityin a developer (for a negative-tone resist). When the exposing dose ofthe lithography exposing process reaches a dose threshold, the exposedresist material will be dissoluble in the developer or alternatively theexposed resist material will be insoluble in the developer. In oneexample, the blocking group 204 includes a t-butoxycardbonyl (tBOC) 500illustrated in FIG. 5.

The resist material 200 further includes a sensitizer 206 to increasethe sensitivity and efficiency of the resist material. The sensitizer206 is designed to increase the sensitivity of the resist material. Aresist material may not be sensitive to EUV but is more sensitive toelectrons or other radiation, such UV or DUV. Thus, by incorporating thesensitizer 206, the resist material has an enhanced sensitivity to thefirst radiation. Particularly, the sensitizer 206 is sensitive to thefirst radiation and be able to generate a second radiation in responseto the first radiation. In the present embodiment, the first radiationis EUV radiation and the second radiation is electron(s). The sensitizer206 absorbs EUV radiation and generates secondary electron. Furthermore,the acid generating compound 208 is sensitive to the secondary electron,absorbs the secondary electron and generates acid.

In some embodiments, the sensitizer 206 is mixed with the polymer 202and PAG 208 in the solvent 210. In some embodiments, the sensitizer 206is alternatively or additionally bonded to the polymer 202 or the PAG208. In various examples, the sensitizer 206 may be monomer additive,oligomer and polymer type in photoresist.

According to one example of principles described herein, the sensitizerincludes a heterocyclic ring that includes at least one nitrogen atomand at least one double bond. In some examples, the sensitizer has arecombination energy within a range of about 165-170 kilocalories/mol.FIGS. 3A and 3B illustrate various double bonds 304 between a nitrogenatom 306 and R 302, which may be a C4˜C30 resonance ring, aromatic, orheterocyclic aromatic. R 302 may also can contain a polar group such as—OH, —NH2, —COOH, —CONH2. Such a structure provides the sensitizer 206with a lower ionization energy and higher recombination energy. FIG. 3Aillustrates an example in which there is one nitrogen atom bonded to aresonance ring. FIG. 3B illustrates an example in which there are twonitrogen atoms bonded to a resonance ring.

The resist material 200 includes an acid generating compound (AGC) 208,such as photoacid generator (PAG), so also referred to as PAG 208. Theacid generating compound 208 absorbs radiation energy and generatesacid. The resist material 200 also includes a solvent 210. The polymer202 and the acid generating compound 208 are mixed in the solvent 210before the resist material is applied to a workpiece, such as asemiconductor wafer, during a lithography process.

The PAG 208 includes a phenyl ring. In a particular example, the PAG 208includes a sulfonium cation, such as a triphenylsulfonium (TPS) group;and an anion, such as a triflate anion. Particularly, the cation of thePAG has a chemical bond to a sulfur and an additional chemical bond suchthat the sensitivity (or absorption) of the PAG to the electron, orother type of the second radiation, is increased.

In some embodiments, the PAG 208 is designed with chemical structure toeffectively absorb EUV radiation. For examples, the PAG 208 may includefluorine, saturated alkyl group, aromatics, heterocyclic group or acombination to enhance the EUV absorption. In some examples, thesensitizer 206 is chemically bonded to PAG 208.

In some examples, the PAG 208 is designed to have specific chemicalstructures to better absorb electrons generated by the sensitizer 206.Specifically, the PAG may include at least one heterocyclic ring havingat least one nitrogen or oxygen atom in addition to several carbonatoms. The PAG 208 may also have at least one double bond within thatheterocyclic ring. Various examples of such PAG structures are shown inFIGS. 7A-7D as well as FIGS. 8A-8H.

FIGS. 7A-7D illustrate PAG structures that have a structure M+ that issurrounded by a number of heterocyclic structures. Such heterocyclicstructures are indicated by R1, R2, R3, R4, R5, R6, and R7. R1, R2, R3,R4, R5, R6, and R7 may include at least one of C1˜C20 heterocyclicaromatics derivatives (e.g., Furan, Pyridine, Pyrazine, Imidazole,thiophene) and fluoro alkyl groups. In some examples, M may be a cationand A may be an anion. In some examples, M or A may be one of Sulfur(S), Carbon (C), or Iodine (I).

FIGS. 8A-8H illustrate various PAG structures that have a structuresurrounded by a number of rings. In the present example, the structureis a sulfur cation. As illustrated, each structure has at least oneheterocyclic ring with at least one double bond. In some examples, thereare at least two double bonds. In some examples, there are three doublebonds.

FIG. 9 is a flowchart showing an illustrative method of using aphotoresist having a sensitizer that improves the photoresist'ssensitivity to EUV light. According to one example, the method includesa process 902 for forming a photoresist layer over a substrate, whereinthe photoresist layer includes a polymer, a sensitizer, and a photo-acidgenerator (PAG), wherein the sensitizer includes a resonance ring thatincludes nitrogen and at least one double bond. For example, thesensitizer may have a structure like the ones illustrated in FIGS. 6Aand 6B. The method further includes a process 904 for performing anexposing process to the photoresist layer. Such an exposing process maybe as described above in the text accompanying FIG. 1B. The methodfurther includes a process 906 for developing the photoresist layer,thereby forming a patterned photoresist layer. The developing processmay be as described above in the text accompanying FIG. 1C.

FIG. 10 is a flowchart showing an illustrative method of using aphotoresist having a PAG that improves the photoresist's sensitivity toEUV light. According to one example, the method 1000 includes a process1002 for forming a photoresist layer over a substrate, wherein thephotoresist layer includes a polymer, a sensitizer, and a photo-acidgenerator (PAG), wherein the sensitizer includes a resonance ring thatincludes nitrogen and at least one double bond. The PAG may have astructure like the structures illustrated in FIGS. 7A-7D and FIGS.8A-8H. The method further includes a process 1004 for performing anexposing process to the photoresist layer. Such an exposing process maybe as described above in the text accompanying FIG. 1B. The methodfurther includes a process 1006 for developing the photoresist layer,thereby forming a patterned photoresist layer. The developing processmay be as described above in the text accompanying FIG. 1C.

The present disclosure provides a photoresist material with enhancedsensitivity and a lithography method using the same. The resist materialincludes a polymer, a sensitizer and a PAG mixed in a solvent. Morespecifically, the PAG includes a chemical structure for increased EUVabsorption or the sensitizer has a chemical structure for increased EUVabsorption. Accordingly, the sensitivity of the resist material isenhanced.

According to one example, a method includes forming a photoresist layerover a substrate, wherein the photoresist layer includes a polymer, asensitizer, and a photo-acid generator (PAG), wherein the sensitizerincludes a resonance ring that includes nitrogen and at least one doublebond. The method further includes performing an exposing process to thephotoresist layer. The method further includes developing thephotoresist layer, thereby forming a patterned photoresist layer.

According to one example, a method includes forming a photoresist layerover a substrate, wherein the photoresist layer includes a polymer, asensitizer, and a photo-acid generator (PAG), wherein the PAG comprisesan absorb group that includes a structure with a plurality of rings, inwhich one of the rings is a heterocyclic resonance ring with at leastone double bond. The method further includes performing an exposingprocess to the photoresist layer. The method further includes developingthe photoresist layer, thereby forming a patterned photoresist layer.

According to one example, a method includes forming a photoresist layerover a substrate. The photoresist layer includes a polymer, a sensitizerthat includes a resonance ring that includes nitrogen and at least onedouble bond, and a photo-acid generator (PAG), wherein the PAG comprisesan absorb group that includes a structure with a plurality of rings, inwhich one of the rings is a heterocyclic resonance ring with at leastone double bond. The method further includes performing an exposingprocess to the photoresist layer and developing the photoresist layer,thereby forming a patterned photoresist layer.

The foregoing outlines features of several embodiments so that those ofordinary skill in the art may better understand the aspects of thepresent disclosure. Those of ordinary skill in the art should appreciatethat they may readily use the present disclosure as a basis fordesigning or modifying other processes and structures for carrying outthe same purposes and/or achieving the same advantages of theembodiments introduced herein. Those of ordinary skill in the art shouldalso realize that such equivalent constructions do not depart from thespirit and scope of the present disclosure, and that they may makevarious changes, substitutions, and alterations herein without departingfrom the spirit and scope of the present disclosure.

What is claimed is:
 1. A method comprising: forming a photoresist layerover a substrate, wherein the photoresist layer includes a polymer, asensitizer, and a photo-acid generator (PAG), wherein the sensitizerincludes a resonance ring that includes nitrogen and at least one doublebond; performing an exposing process to the photoresist layer; anddeveloping the photoresist layer, thereby forming a patternedphotoresist layer.
 2. The method of claim 1, wherein the sensitizer ischemically bonded to the PAG.
 3. The method of claim 1, wherein theresonance ring includes at least two nitrogen atoms.
 4. The method ofclaim 1, wherein the sensitizer includes a second resonance ringcontaining nitrogen and at least one double bond.
 5. The method of claim1, wherein the sensitizer has an electron recombination energy within arange of about 165-170 kilocalories/mol.
 6. The method of claim 1,wherein the sensitizer is an aromatic structure.
 7. The method of claim1, wherein the sensitizer includes a heterocyclic structure.
 8. Themethod of claim 1, wherein the sensitizer includes a polar group of atleast one of —OH, —NH2, COOH, and CONH2.
 9. The method of claim 1,wherein the PAG comprises an absorb group that includes a structure witha plurality of rings, wherein at least one of the rings is heterocyclicand includes at least one double bond.
 10. The method of claim 9,wherein the structure includes one of: sulfur, iodine, or carbon.
 11. Amethod comprising: forming a photoresist layer over a substrate, whereinthe photoresist layer includes a polymer, a sensitizer, and a photo-acidgenerator (PAG), wherein the PAG comprises an absorb group that includesa structure with a plurality of rings, in which one of the rings is aheterocyclic resonance ring with at least one double bond; performing anexposing process to the photoresist layer; and developing thephotoresist layer, thereby forming a patterned photoresist layer. 12.The method of claim 11, wherein the absorb group comprisesTriphenylsulfonium triflate (TPS).
 13. The method of claim 11, whereinthe absorb group further includes at least one of fluorine, a saturatedalkyl group, an aromatic structure, and a heterocyclic group chemicallybonded to the TPS.
 14. The method of claim 11, wherein the heterocyclicresonance ring includes at least one carbon atom and at least one of:oxygen or nitrogen.
 15. The method of claim 11, wherein the sensitizerfurther includes a resonance ring that includes nitrogen and at leastone double bond.
 16. The method of claim 15, wherein the sensitizerincludes a polar group of at least one of —OH, —NH2, COOH, and CONH2.17. The method of claim 15, wherein the resonance ring includes at leasttwo nitrogen atoms.
 18. A method comprising: forming a photoresist layerover a substrate, wherein the photoresist layer includes: a polymer; asensitizer that includes a resonance ring that includes nitrogen and atleast one double bond; and a photo-acid generator (PAG), wherein the PAGcomprises an absorb group that includes a structure with a plurality ofrings, in which one of the rings is a heterocyclic resonance ring withat least one double bond; performing an exposing process to thephotoresist layer; and developing the photoresist layer, thereby forminga patterned photoresist layer.
 19. The method of claim 18, wherein thePAG includes a heterocyclic ring with at least two double bonds and anoxygen atom.
 20. The method of claim 18, wherein the PAG includes aheterocyclic ring with at least two double bonds and a nitrogen atom.